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Risk Management Activities - Non-Hedges (Details) € in Millions, $ in Millions, $ in Millions, $ in Millions | Dec. 31, 2020 CAD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2020 AUD ($) | Dec. 31, 2020 EUR (€) | Dec. 31, 2019 CAD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2019 AUD ($)
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Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Hedging instrument, assets | $ 2 |  |  |  | $ 7 |  |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021-2024, Contract One |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Hedging instrument, liabilities | (14) |  |  |  |  |  |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021-2024, Contract Two |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Hedging instrument, assets | 9 |  |  |  |  |  |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021, Contract One |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Hedging instrument, assets | 0 |  |  |  |  |  |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021, Contract Two |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Hedging instrument, assets | 0 |  |  |  |  |  |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2020-2023, Contract One |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Hedging instrument, assets |  |  |  |  | 0 |  |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2020-2023, Contract Two |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Hedging instrument, liabilities |  |  |  |  | (4) |  |
Foreign exchange forward contracts – foreign-denominated debt | Discontinued Hedge Positions | Currency risk | Maturity, 2022 |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Hedging instrument, assets | 2 |  |  |  | 6 |  |
Australia, Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021-2024, Contract One |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Notional amount sold |  |  | $ 197 |  |  |  |
Australia, Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021, Contract One |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Notional amount sold |  |  | $ 4 |  |  |  |
Australia, Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2020-2023, Contract One |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Notional amount sold |  |  |  |  |  |  | $ 286
Canada, Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021-2024, Contract One |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Derivative, notional amount purchased | 181 |  |  |  |  |  |
Canada, Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021-2024, Contract Two |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Derivative, notional amount purchased | 72 |  |  |  |  |  |
Canada, Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021, Contract Two |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Notional amount sold | 1 |  |  |  |  |  |
Canada, Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2020-2023, Contract One |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Derivative, notional amount purchased |  |  |  |  | 266 |  |
Canada, Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2020-2023, Contract Two |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Derivative, notional amount purchased |  |  |  |  | 139 |  |
Canada, Dollars | Foreign exchange forward contracts – foreign-denominated debt | Discontinued Hedge Positions | Currency risk | Maturity, 2022 |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Notional amount sold | $ 191 |  |  |  | $ 191 |  |
Derivative, notional amount purchased |  | $ 150 |  |  |  | $ 150 |
U.S. Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021-2024, Contract Two |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Notional amount sold |  | 47 |  |  |  |  |
U.S. Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021, Contract One |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Derivative, notional amount purchased |  | $ 3 |  |  |  |  |
U.S. Dollars | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2020-2023, Contract Two |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Notional amount sold |  |  |  |  |  | $ 108 |
Euro Member Countries, Euro | Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk | Maturity, 2021, Contract Two |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |
Derivative, notional amount purchased | € |  |  |  | € 1 |  |  |

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